Optical transmission system constructing method and system

ABSTRACT

An optical transmission system accomplishes optical transmission to a long distance by combining a multiplexing line terminal with optical amplifiers, linear repeaters, and regenerators with optical amplifiers combined together. The system also accomplishes the optical transmission to a short distance by directly connecting the linear terminals therebetween, with an electric-to-optic converter replaced by an electric-to-optic converter having a semiconductor amplifier, with an optic-to-electric converter by an optic-to-electric converter having an avalanche photodiode as light receiver, an with no use of any optical booster amplifier and optical preamplifier in the multiplexing line terminal. With these, the optical transmission system can be easily constructed depending on the transmission distance required.

[0001] This is a continuation of application Ser. No. 09/409,872 filedOct. 1, 1999, U.S. Pat. No. 6,266,169, which is a continuation ofapplication Ser. No. 09/244,856 filed Feb. 5, 1999, U.S. Pat. No.6,018,405, which is a continuation of application Ser. No. 08/746,027filed Nov. 5, 1996, U.S. Pat. No. 5,875,046, which is a continuation ofapplication Ser. No. 08/705,366 filed Aug. 29, 1996, U.S. Pat. No.5,812,289, which is a continuation of 08/044,425 filed Apr. 7, 1993,U.S. Pat. No. 5,555,477, which is a CIP of 08/023,546 filed Feb. 26,1993, U.S. Pat. No. 5,500,756.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the invention

[0003] The present invention relates to an optical transmission methodand system for carrying data transmission with use of optical fiber.More particularly, it concerns an optical transmission method and systempreferable in high-speed data transmission to a long distance.

[0004] 2. Description of the Prior Art

[0005] Prior arts related to the optical transmission system include,for example, the technique disclosed in the Japanese Patent ApplicationLaid-Open 3-296334.

[0006] However, it is demanded to accomplish an optical transmissionsystem operating at further higher speed since development of the moderninformation society has increased long-distance communication traffic inrecent years. Also, it is desired that the optical transmission systemcan transmit data to further longer distance without repeat in view ofreliability and cost of the system.

[0007] Furthermore, the number of fields to which an opticaltransmission system is applied has been increased with the recentdevelopment of the information society. For the reason, it is needed toaccomplish the optical transmission system having a variety of functionsand capacities to satisfy specific requirements.

SUMMARY OF THE INVENTION

[0008] In view of the foregoing, it is an object of the presentinvention to provide an optical transmission system constructing methodcapable of easily constructing an optical transmission method and systemdepending on required functions and capacities.

[0009] Briefly, the foregoing object is accomplished in accordance withaspects of the present invention by an optical transmission system. Theoptical transmission system is characterized in constructing a lineterminal having multiplexing means for multiplexing signals anddemultiplexing means for demultiplexing the multiplexed signal so thatto serve as a transmitter, the line terminal is selectively capable ofimplementing either a first combination of an electric-to-opticconverter circuit for converting the electric signal multiplexed by themultiplexing means to a transmission light with an optical fiberamplifier for amplifying the transmitting light before feeding into anoptical transmission medium or electric-to-optic converting means havinga semiconductor optical amplifier for converting the electric signalmultiplexed by the multiplexing means to a transmission light beforefeeding an optical transmission line. The optical transmission systemalso is characterized in constructing the line terminal so that to serveas a receiver, the line terminal is selectively capable of implementingeither a second combination of an optical fiber amplifier for amplifyinga receiving light from an optical transmission medium with anoptic-to-electric converter circuit for converting the amplifiedreceiving light to electric signal before feeding to the demultiplexingmeans or an optic-to-electric converting means for converting thereceived light from the optical transmission medium to electric signalbefore feeding to the demultiplexing means with an avalanche photodiodeused as light receiver.

[0010] Also, the optical transmission system is characterized inconstructing the optical transmission system for use as a longdistanceoptical transmission system, a plurality of the line terminals havingthe first combination to serve as the transmitter and the secondcombination to serve as the receiver implemented therein each areconnected to the optical transmission medium through a single or aplurality of repeaters inserted in the optical transmission medium formultiplying the optical light signal on the optical transmission medium.

[0011] Further, the optical transmission system is characterized inconstructing the optical transmission system for use as a shortdistanceoptical transmission system, the plurality of the line terminals havingthe electric-to-optic converting means having a semiconductor opticalamplifier therein to serve as the transmitter and the optic-to-electricconverting means having the avalanche photodiode used as the lightreceiver to serve as the receiver implemented therein each are directlyconnected to the optical transmission line.

[0012] The optical transmission system constructing method of thepresent invention enable an easy construction of any of thelong-distance an short-distance optical transmission system only byselecting desired types of the transmitters and receivers to beimplemented to change the combinations of the units. This is because theline terminal is constructed so that to serve as the transmitter, theline terminal is selectively capable of implementing either the firstcombination of an electric-to-optic converter circuit for converting theelectric signal multiplexed by the multiplexing means to thetransmission light with an optical fiber amplifier for amplifying thetransmitting light before feeding into an optical transmission medium orelectric-to-optic converting means having the semiconductor opticalamplifier for converting the electric signal multiplexed by themultiplexing means to the transmission light before feeding an opticaltransmission line, and that to serve as the receiver, the line terminalis selectively capable of implementing either the second combination ofan optical fiber amplifier for amplifying the receiving light from anoptical transmission medium with an optic-to-electric converter circuitfor converting the amplified receiving light to electric signal beforefeeding to the demultiplexing means or an optic-to-electric convertingmeans for converting the received light from the optical transmissionmedium to electric signal before feeding to the demultiplexing meanswith an avalanche photodiode used as light receiver.

[0013] The foregoing and other objects, advantages, manner of operationand novel features of the present invention will be understood from thefollowing detailed description when read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the accompanying drawings:

[0015]FIG. 1 is a block diagram for a functional construction of aoptical transmission system of an embodiment of the present invention.

[0016]FIG. 2 is an overall configuration for a network system related tothe embodiment.

[0017]FIG. 3 is a configuration for a network among a large-scaleswitching nodes extracted from the network system.

[0018]FIG. 4 is a configuration for a network among a small-scaleswitching nodes and among a small-scale switching nodes and the largescale switching node extracted from the network system.

[0019]FIG. 5 is a configuration for a network for a metropolitan areaextracted from the network system.

[0020]FIG. 6 is block diagrams for a functional construction of a node.

[0021]FIG. 7 is a hierarchical construction of a network system.

[0022]FIG. 8 is a frame construction for a multiplexing frame used inthe network system.

[0023]FIG. 9 is logical positions of path groups.

[0024]FIG. 10 is a bit allocation of overhead of the path groups.

[0025]FIG. 11 is an example of setting the path group in a ring.

[0026]FIG. 12 is path group switching procedures at failure.

[0027]FIG. 13 is a typical sequence of switching requests.

[0028]FIG. 14 is a block diagram for a configuration of the networksystem related to the embodiment.

[0029]FIG. 15 is a sequence diagram for transfer of alarms in thenetwork system.

[0030]FIG. 16 is a block diagram for the optical transmission system fora long distance system.

[0031]FIG. 17 is a block diagram for the optical transmission system fora short distance system.

[0032]FIG. 18 is a block diagram for a clock transit system for theoptical transmission system.

[0033]FIG. 19 is bytes to be scrambled of an overhead in a STM-64section.

[0034]FIG. 20 is a block diagram for the 1R-REP.

[0035]FIG. 21 is a block diagram for a board construction of the 1RREP.

[0036]FIG. 22 is a format for a surveillance and control signal for usein the surveillance and control of the 1R-REP.

[0037]FIG. 23 is a block diagram for an inter-office transmission lineinterface of the LT-MUX.

[0038]FIG. 24 is a block diagram for the intra-office transmission lineinterface of the LT-MUX.

[0039]FIG. 25 is a relationship of multiplex and demultiplex between aSTM-64 frame and a STM-1×64 supported by the LT-MUX.

[0040]FIG. 26 is a block diagram for a transmitter of the LT-MUX formingthe long distance system.

[0041]FIG. 27 is a block diagram for the transmitter of the LT-MUXforming the short distance system.

[0042]FIG. 28 is a block diagram for a receiver of the LT-MUX formingthe long distance system.

[0043]FIG. 29 is a block diagram for the receiver of the LT-MUX formingthe short distance system.

[0044]FIG. 30 is a block diagram for a node having LT-MUXes and an ADMswitch used.

[0045]FIG. 31 is a block diagram for extracted parts serving to thesurveillance and control system for the LT-MUX.

[0046]FIG. 32 lists features of the functional blocks of thesurveillance and control system.

[0047]FIG. 33 is a block diagram for a redundancy configuration of atransmitting system in the LT-MUX.

[0048]FIG. 34 is a block diagram for the redundancy configuration of areceiving system in the LT-MUX.

[0049]FIG. 35 is a block diagram for construction of a hitless switchingprocess feature section for transmission line.

[0050]FIG. 36 is a block diagram for a construction of a 3R-REP.

[0051]FIG. 37 is a front view for an implementation of the 1R-REP.

[0052]FIG. 38 is structures of a optical preamplifier and opticalbooster amplifier forming a single 1R-REP system.

[0053]FIG. 39 is a front view for an implementation of the LT-MUX.

[0054]FIG. 40 is a front view for an implementation of two systems ofthe LT-MUX in a single rack without the line redundancy configuration.

[0055]FIG. 41 is a front view for an implementation of the LT-MUX forconstructing the small scale switching node with a 40G switch unit builtin as shown in FIG. 6b.

[0056]FIG. 42 is a structural view for a 40G switch.

[0057]FIG. 43 is a front view for an implementation of the LT-MUX forconstructing the large scale switching node.

[0058]FIG. 44 is a front view for an implementation of the 3R-REP.

DETAILED DESCRIPTION OF THE INVENTION

[0059] The following describes an embodiment according to the presentinvention for the optical transmission system by reference to theaccompanying drawings.

[0060] 1. General Description

[0061] First, this section outlines the optical transmission system ofthe embodiment.

[0062]FIG. 1 is a block diagram for the functional construction of theoptical transmission system of the embodiment.

[0063] The optical transmission system, as shown in FIG. 1a, is anultralong distance transmission system for making optical transmissionbetween line terminals with multiplexers (hereinafter referred to as theLT-MUX 1) or between the LT-MUX 1 and a regenerator (hereinafterreferred to as the 3R-REP 3) with use of an optical amplifier repeater(hereinafter referred to as the 1R-REP 2). The system can send the dataat 10 Gb/sec through an optical fiber 40 up to 320 km by the 3R-REP 3 atthe longest intervals of 80 km by the 1R-REP 2.

[0064] The LT-MUX 1 makes a multiplex and section-termination-process(12) of the data received by an intra-office interface 11 providedtherein, and converts them to optical signal (13). An optical boosteramplifier 14 magnifies the optical signal before feeding it into anoptical transmission medium. On the contrary, the data received from theoptical transmission medium is magnified by an optical preamplifier 15before being converted to electrical signal (16). The signal then isdemultiplexed and section-termination-processed (12) before beingdistributed to the intra-office interfaces 11. The 1R-PEP 2 repeats theoptical signal in a way that any of optical fiber amplifiers 21 and 22magnifies the optical signal received from the optical transmissionmedium before feeding it out. The 3R-REP 3 regenerates the data torepeat in a way that the data received from the optical transmissionmedium are magnified by an optical preamplifier 35 before beingconverted to electrical signal (36). The electrical signal then isdemultiplexed and section-termination-processed (32) and is multiplexedand section-termination-processed (32) again. It further is converted tooptical signal (33) and magnified by an optical booster amplifier 34before being fed into the optical transmission medium. The interface ofany equipment with the optical transmission medium (hereinafter referredto as the inter-office interface) is equivalent to the CCITT recommendedsynchronous transport modulelevel N (STM-N) where N=64, and uses ascrambled binary NRZ (non-return to zero) as transmission line code. Aspectrum broading is used to prevent a stimulated Brillouin scatteringdue to a higher power output.

[0065] The intra-office interface 11 of the LT-MUX 1 can contain aseries of STM-1 (150 Mb/sec) by 64 or a series of STM-4 (600 Mb/sec) by16. Note that the series of STM-4 (600 Mb/sec) by 1 can be compatiblewith the series of STM-1 by 4.

[0066] The optical transmission system can be configured in another waythat instead of the 1R-REP 2 shown in FIG. 1a, the LT-MUXes 1 aredirectly connected together or the LT-MUX 1 is directly connected withthe 3R-REP 3. In this case, the transmission distance is up to 120 kmwithout repeater.

[0067] Also, the optical transmission system can be configured in stillanother way as that shown in FIG. 1b, the 1R-REP 2, the optical boosteramplifier 14, and the optical preamplifier 15 are omitted, but LT-MUXes1 having an opto-electric converter 2000 and an electro-optic converter2010 which are different in the characteristics from those of the LT-MUX1 in FIG. 1a are directly connected together. In this case, the outputlevel is around +6 dBm, and the transmission distance is up to 80 kmwithout repeater.

[0068] The optical transmission system having the LT-MUX 1, the 3R-REP3, the optical booster amplifier 14, and optical preamplifier 15 iscalled the long-distance system below; and the optical transmissionsystem having no optical booster amplifier 14 and optical preamplifier15 in the LT-MUX 1 and 3R-REP 3 is called the short distance systembelow.

[0069] 2. Overall System Configuration

[0070] In turn, this section describes a network system having theoptical transmission system of the embodiment.

[0071]FIG. 2 is an overall configuration for a network system related tothe embodiment.

[0072] In the figure are indicated a large scale switching node 110having the LT-MUX 1 of the embodiment and a small scale switching node120 having the LT-MUX 1 of the embodiment.

[0073] The large-scale switching nodes 110 in the network system relatedto the embodiment, as shown in the figure, are directly connectedtherebetween in a ladder-shaped structure with use of the 1R-REP 2 andthe 3R-REP 3. The network system has routes diversed therein and theCCITT recommended VC-¾ path protection switch in the meshed network,thereby increasing reliability of the network. The small-scale switchingnodes 120 are ringstructured, and the small-scale switching nodes 120and the large scale switching nodes 110 are also ring-structured. Thisdoes not only provide a multiplexing effect that allows efficient use ofthe large-capacity transmission medium, but also keeps two routes thatcan increase the reliability. In addition, a metropolitan area has amultiple of rings that can increase the reliability in, an area ofrelatively narrow, but large, facial extending traffic.

[0074]FIG. 3 is a configuration for a network among the large-scaleswitching nodes 130 extracted from the network system.

[0075] The large-scale switching nodes 130, as shown in the figure, aredirectly connected thereamong with use of the 1R-REPs 2 and the 3R-REPs3 without switching through an intermediate node, thereby decreasing theline cost. A distance between the 1R-REPs 2 is up to 80 km in view ofthe S/N design, and the one between the 3RREPs 3 is up to 320 km in viewof the nonlinear distortion of the fiber.

[0076]FIG. 4 is a configuration for a network among the small-scaleswitching nodes 120 and among the small-scale switching nodes 120 andthe large scale switching nodes 110 extracted from the network system.

[0077] If a distance between the small-scale switching nodes 120 isshorter than 120 km, as shown in the figure, no repeaters are used, butdirect connection is made between any two of the smallscale switchingnodes 120. If the distance exceeds 120 km, the 1R-REP 2 is used to makethe long distance system as mentioned previously. If the distance isshorter than 80 km, as will be described in detail later, the 10 Gb/sectransmitter is replaced by the one made up of a semiconductor opticalamplifier and an APD (avalanche photodiode) to form a further economicshort distance system (FIG. 1b).

[0078]FIG. 5 is a configuration for a network for the metropolitan areaextracted from the network system.

[0079] The metropolitan area, as shown in the figure, has a plurality ofadjoining rings formed of the transmission media connecting the nodes ina meshed network, thereby accomplishing efficient multiplex operationand high reliability. It should be noted that there will be a greaternumber of the shorter node distances than 80 km. Then, as describedabove, the short distance system is made up of the semiconductor opticalamplifier and the APD to form the network at low cost.

[0080]FIG. 6 is block diagrams for the functional construction of thenode.

[0081] The large scale switching node 110, as shown in FIG. 6a, has twoLT-MUXes 1 and a VC-¾ cross-connection switch 111 for path switching andsetting at the VC-¾ level in the synchronous digital hierarchy (SDH).The two LT-MUXes 1 are connected by a high-speed interface which will bedescribed later, but not any intra-office interface. The large scaleswitching node 110 also has the STM-1 interface and the STM-4 interfaceas the intraoffice interfaces. These interfaces can connect a linerepeater terminal 5000 for transmission between a 600 Mb/sec or 2.4Gb/sec offices, a cross-connection equipment 5100 for terminating theintra-office interface 111, and an ATM cross-connection switch 5200. TheATM cross-connection switch 5200, if used, can accomplish lower cost anddecrease cell delay as the 600 Mb/sec intra-office interface is used.Note that the large scale switching node 110 can be alternatively madeup of the two LTMUXes 1 and a cross-connect equipment 111.

[0082] The small scale switching node 120 is the same as the large scaleswitching node 110 or as shown in FIG. 1b, has the LT-MUX 1 and an VC-¾add-drop multiplex (ADM) switch. The small scale switching node 120also, like the large scale switching node 110, has the STM-1 interfaceand the STM-4 interface as the intraoffice interfaces, which can connectthe line repeater terminal 5000 for transmission between a 600 Mb/sec or2.4 Gb/sec offices, the cross-connection equipment 5100 for terminatingthe intraoffice interface 111, and the ATM cross-connection switch 5200.

[0083] The intra-office interface 11 of the LT-MUX 1 is used for theSTM-1 interface and the STM-4 interface for each node.

[0084] Table 1 shows a hierarchy of the network system and terminals atthe respective hierarchy level. TABLE 1 NO. LEVEL TERMINAL OVERHEAD 1VC-¾ VC-½ processors, and VC-¾ POH 2 VC-¾ path VC-¾ cross-connector Z3byte of group (virtual ring branch - representing (VC-¾ PG) insertionpoint) VC-¾ POH 3 STM-64 section LT-MUX MSOH section 4 Regenerator3R-REP and LT-MUX RSOH section 5 Linear repeater 1R-REP, 3R-REP, LT-MUXWavelength section multiplexed management signal

[0085] As shown in the table, the present embodiment defines the new VC¾path group to accomplish easy path switching at failure of anytransmission medium.

[0086]FIG. 8 is a frame construction for an STM-64 which is aninter-office interface.

[0087] The overhead for the VC-¾ path group, as shown in the figure, isthe Z3 byte of the representing VC-¾ POH forming the VC-¾ path group.

[0088] The following describes the path switching with use of the pathgroup at failure of any transmission medium.

[0089] The term “path group” as used herein denotes a set of partswithin a ring of the VC-¾ path that a point of insertion into a virtualring is equal to each other and a point of branch from the virtual ringis equal to each other. The term “virtual ring” as used herein denotes aring extracted from the network as a part which can virtually form aring-like path. It should be noted that as shown in FIG. 9, the pathgroup is positioned between section and path layer in view of thenetwork layer structure.

[0090] The embodiment switches the path group when the path group is atfailure. The path group is managed with use of the Z3 byte of therepresenting VC-¾ path overhead within the path group. FIG. 10 is a bitallocation of the Z3 byte. The path group failure is detected by a pathgroup alarm indication signal (PGAIS) defined in the Z3 byte.

[0091] Table 2 shows path switching features in the embodiment. TABLE 2NO. ITEM DESCRIPTION 1 Switching unit VC-¾ path group (set of VC-¾ pathsin same route within ring) 2 Switching net- Virtual ring (on VC-¾ worktopology path mesh) 3 Protection form 1 + 1 bidirectional switching(Working path group and protection group are turned reversely on ring.)4 Switching control Autonomous switching to ground office method in ringby APS control for path group 5 APS byte b1 to b4 of Z3 byte path grouprepresenting VC-¾ 6 APS protocol Conform to 1 + 1 switching protocol ofsection APS 7 Switching trigger Path group AIS reception at path groupterminal point (Path group AIS bit in Z4 type = 1) 8 Switching VC-¾cross-connection switch (LT-MUX equipment with XC and LT-MUX with ADM) 9Switch control Switching ACM* meshed network in units method of VC.

[0092] As shown in Table 2 above, the embodiment uses an alternativemeshed network switching to increase the reliability. Controlling themesh switching in the embodiment is the autonomous switching in units ofthe VC-¾ path group virtual ring, which conforms to the section APSrecommended by CCITT.

[0093]FIG. 11 is an example of setting the path group in the ring. Theprotection path group is extended in the direction reverse to theworking one.

[0094]FIG. 12 is path group switching procedures at failure. FIG. 13 isa typical sequence of switching requests. The switching sequence, asshown in FIG. 13, conforms to the usual 1+1 section APS. Finally, Table3 shows priorities of the switching requests and coding of the Z3 byte,and Table 4 shows coding of the path group status. TABLE 3 TYPE OF z3BYTE PRIOR- SWITCHING b1, b2, ITY REQUEST DESCRIPTION b3, b4 1 LockoutInhibit all switchings by any — of following switching requests, withworking state held. 2 Forced Make switching if protection 1 1 1 0switching path group is normal. (FS) 3 Signal Make switching ifprotection 1 1 0 0 failure path group is normal after (SF) results ofsurveillance of working path group AIS and units are triggered forfailure. Path group AIS is generated by LOS, LOF, and severed MER. 4Manual Make switching if protection 1 0 0 0 switching path group isnormal. 5 Wait to Do not release from switched 0 1 1 0 restore stateduring the waiting period even if the working path group is restoredwhile the automatic switching SF or SD is made. 6 Exerciser Testswitching control system. 0 1 0 0 7 Reverse Respond operation ofswitching 0 0 1 0 request to requesting source after receiving requestfor forced switching or signal failure or wait to restore. 8 No bridgeInhibit all switchings by any 0 0 0 0 required of the followingswitching requests, with the working state held.

[0095] TABLE 4 z3 BYTE b7, b8 DESCRIPTION 0 0 Normal state 1 1 PG-AIS* 10 PG-FERF

[0096] 3. Surveillance and Control System

[0097] This section describes a surveillance and control system for thenetwork system related to the embodiment.

[0098]FIG. 14 is a block diagram for a configuration of the networksystem related to the embodiment.

[0099] Each of the LT-MUXes and the 1R-REPs 2 has a surveillance andcontrol function 1001 and an OpS-IF 1002 for connection with an OpS(operation system) 1000. The surveillance and control are made undercontrol of the OpS 1000 which governs the surveillance and control ofthe system.

[0100] The embodiment makes a wavelength multiplex of a surveillance andcontrol signal with a main signal on the STM-64 interface beforetransmitting the multiplexed signal to monitor and control the1R/3R-REPs 3 having no OpS IF 1002 remotely. That is, the OpS 1000 givesa direction signal to the equipment having the OpS IF 1002 to make theequipment superimpose the direction signal onto the surveillance andcontrol signal, or makes the 1R/3R-REP having no OpS IF 1002 transfer analarm detected or generated by the 1R/3R-REP to the equipment having theOpS IF 1002. Alternatively, it can be made that the 1R/3R-REP shouldhave the OpS IF 1002 to allow the OpS 1000 to monitor and control the1R/3R-REP directly.

[0101] In turn, the surveillance and control signal of 384 kb/sec istransferred by a light of the same 1.48 μm wavelength as that of apumping light source of the 1R-REP 2. The surveillance and controlsignal, as shown in FIG. 22, also has a 48 byte frame length for a 1msec frame period, 24 bytes (192 kb/sec) of which are allocated to a DCC(data communication channel) for the remote control, 8 bytes (64 kb/sec)for an order wire, and 6 bytes (48 kb/sec) for the alarm transfer. Thesurveillance and control signal allows each of the 1R/3R-REPs 2 toinform the state and alarm. That is, each of the 1R/3R-REPs can generateits own monitoring information and repeat the surveillance and controlsignal generated by the preceding 1R/3P-REP as well. The statemonitoring is made at intervals of 1 sec so that an access collisioncannot happen even if number of the 1R/3RREPs is around 100.

[0102] Also the surveillance and control signal has 1 byte allocatedthere to as the 1R-REP section has a feature equivalent to that of theusual AIS. The 1R/3R-REP having detected a fatal failure, such as lossof the main signal, transfers its own ID to the succeeding repeaterusing the one byte. This 1R/3R-REP 2 repeats the one byte to theLT-MUX 1. This allows informing of the 1R/3R-REP section AIS atintervals of 1 msec. If it is used, the 3R-REP converts it to an S-AIS(section alarm indication signal).

[0103] The features of the surveillance and control system are chartedin Tables 5 and 6. Surveillance and control items are charted in Table7. TABLE 5 ITEM DESCRIPTION NOTE Surveillance (1) LT-MUX 1R/3R-REP andcontrol Has OpS-IF and is started by can have equipment direction byOpS. OpS-IF. (2) 1R-REP Has RMT-IFs, such as DCC-IF and ALARM-IF, and isstarted by direc- tion by surveillance and control signal. (3) 3R-REPSame as 1R-REP. Surveillance (1) Physical characteristics Frame andcontrol Frame length: 48 bytes. synchro- signal Frame period: 1 msec.nization Rate: 384 kb/sec. by CMI Wavelength: 1.48 μm. code rule Linecode: CMI. violation. (2) Generation method To increase Generation byLT-MUX and 1R/3R- reliability. REP. (3) Transfer method Iswavelength-multiplexed with the main signal before being transferred.1R/3R-REP determines either repeat or reception with destination IDadded on surveillance and control signal. For repeat, 1R/3R-REP storesit in the reception buffer before transmission. (4) Access to 1R/3R-REPAccess can be made from either west or east. Monitoring (1) Amount ofinformation: Equivalent method 4 bytes of surveillance and control tofeature signal. of SONET F1 (2) Monitoring Interval/alarm transfer byte.interval: 1 sec. However, if fatal failure, such as loss of signal, isdetected, 1R/3R-REP section AIS is transferred at intervals of 1 msec.(3) Transference can be made to either west and east.

[0104] TABLE 6 ITEM DESCRIPTION NOTE Control (1) Surveillance andcontrol signal Setting can method has DCC area of 24 bytes be made also(equivalent to 192 kb/sec) from OpS if provided therein for settingnecessary. surveillance and control items. (2) Surveillance and controlsignal has order wire area of 8 bytes (equivalent to 64 kb/sec) providedtherein. This allows maintenance communication. (3) Access can be madefrom either west or east. (4) Response is made after execution ofinstruction.

[0105] TABLE 7

Monitoring items Monitoring items Monitoring items In section Opticalfiber Optical fiber Optical fiber monitoring disconnection (LOS)disconnection disconnection (LOS) items Loss of main signal Loss of mainsignal Loss of main signal (Preceding REP (PReceding REP (Preceding REPfailure) failure) failure) Loss of surveilance Loss of surveilance Lossof surveilance and control signal and control signal and control signal(Preceding REP (Preceding REP (Preceding REP failure) failure) failure)Surveilance and Surveilance and Surveilance and control signal LOFcontrol signal LOF control signal LOF (CMI) (CMI) (CMI) Surveilance andSurveilance and Surveilance and control signal FCS control signal FCScontrol signal FCS error error error JR section Main signal LOF Mainsignal LOF monitoring Error rate Error rate items degradation (B1)degradation (B1) F1 byte process F1 byte process S-AI5 detection, S-AI5detection, generation, and generation, and transfer transfer OthersEquiptment failure Equiptment failure Other SOH features Input,intermediate, Input, intermediate, Equiptment failure and output signaland output signal Input, intermediate, levels levels and output signalLD temperature LS temperature levels LD biases LD biases LD temperaturesGains Gains LD biases Gains Control items Control items Control itemsYear and date Year and date Year and date setting setting setting Outputhalt or release Output halt or release Output halt or release Soft strapsetting Soft strap setting and reading related and reading related toSDH to SDH Example: Example: B1 error rate- B1 error rate- degradationthreshold degradation threshold value value Order wire of Order wire ofOrder wire of 64 kb/sec 64 kb/sec 64 kb/sec DCC of 192 kb/sec DCC of 192kb/sec DCC of 192 kb/sec

[0106] As shown in FIG. 7, if any of the monitoring items is at failure,the equipment transfers the alarm. The alarm detection and transfer aremade for the four layers, including the 1R section layer, the 3R sectionlayer, the LT section layer, and the path layer.

[0107] The 1R section layer deals with any of the alarms detected by the1R-REP 2. The alarm is transferred by the surveillance and controlsignal. The 1R section layer processes the following items.

[0108] (a) Optical fiber disconnection: The main signal input and thesurveillance and control signal input are disconnected by an opticalfiber disconnection.

[0109] (b) Loss of main signal: The main signal input is lost by apreceding 1R/3R-REP stage failure.

[0110] (c) Loss of surveillance and control signal: The main signalinput is lost by a preceding 1R/3R-REP stage failure.

[0111] (d) Surveillance and control signal LOF (loss of frame): Theframe synchronization surveillance and control signal is lost.

[0112] (e) Surveillance and control signal FCS (frame check sequence)error: A code error is detected by checking the FCS of the surveillanceand control signal.

[0113] (f) 1R section failure REP identification: The 1R-REP havingdetected a fatal failure writes its own ID into a predetermined byteprovided in the surveillance and control signal before generating thesurveillance and control signal. This accomplishes the feature of F1byte for the SDH recommended by the CCITT.

[0114] The 3R section layer performs processes about an RSOH(regenerator section overhead) of the STM frame.

[0115] (a) Main signal LOF: Loss of frame of the main signal is detectedwith A1 and A2 bytes.

[0116] (b) Error rate degradation: MER and ERR MON are generated withuse of B1 byte.

[0117] (c) F1 byte process: If it detects a fatal failure, the 3R-REPwrites its own ID into the F1 byte of the sending STM frame. Also, if itreceives the surveillance and control signal indicating that thepreceding the 1R-REP is at failure, the 3RREP writes the ID in apredetermined byte into the F1 byte of the sending STM frame.

[0118] (d) S-AIS detection, generation, and transfer: S-AIS process ismade.

[0119] The LT section layer performs processes about an MSOH (multiplexsection overhead) of the STM frame.

[0120] The path layer performs processes about a VC-¾ POH (pathoverhead) of the STM frame.

[0121] In turn, the alarm of the 1R section is sent to the LT-MUXthrough 1R-REP and 3R-REP by the surveillance and control signal.

[0122] For any of the fatal failures, such as loss of the main signal,if the alarm is transferred through the 3R-REP, then the 3R-REP convertsit to S-AIS. FIG. 15 is a sequence diagram for transfer of the alarm inthe network system.

[0123] 4. Optical Transmission System

[0124] This section describes an optical transmission method for theoptical transmission system related to the embodiment.

[0125]FIG. 16 is a block diagram for the optical transmission system forthe long distance system.

[0126] As shown in the figure, the embodiment includes a modulatorintegrated light source module 200 of 1552 nm wavelength having littlechirping as a sending light source for the LT-MUX 1 and the 3RREP 3. Tosuppress an SBS (stimulated Brilloiun scattering) caused in the opticalfiber, the embodiment uses the spectrum broading that a signal of alow-frequency oscillator 201 is applied to a laser section of themodulator integrated light source module 200 to make a light frequencymodulation. Optical booster amplifiers 14 and 34 use a bidirectionpumping method for which a pumping light source of 1480 nm wavelength isused. The transmission power and chirping quantities of a modulator areoptimized to accomplish the longest regeneration distance of 320 km.

[0127] To transmit the supervisory signal, a supervision light source202 of 1480 nm wavelength range provided in the light booster amplifieris used. The supervisory signal is wavelengthmultiplexed with the mainsignal before being transmitted to a downstream. To prevent output ofthe light booster from decreasing, a WDM (wave division multiplex)coupler 203 for wavelength multiplex of the surveillance and controlsignal with the main signal is made to also serve as WDM coupler forlaser pumping.

[0128] A forward pumping optical preamplifier 35 having a pumping sourceof 1480 nm range accomplishes highly sensitive reception.

[0129] On the other hand, to receive the supervisory signal, a WDMcoupler 210 for pumping Erbium-doped fiber is used to draw thesupervisory signal, which is received by an exclusive receiver. Thisminimizes degradation of the NF (noise figure). With the use of thelight booster amplifiers 13 and 34 and light preamplifiers 5 and 35, thedistance between the LT-MUX 1 and the 3R-REP 3 can be made 120 km ifthey are directly connected together.

[0130] The 1R-REP 2 has two Erbium-doped fibers 211 and 216 and pumpinglight sources of 1480 nm wavelength range used therein. The former laserpumping stage 212 pumps forward, and the latter three laser pumpingstages 213, 214, and 215 pump bidirectionally. This accomplishes bothlower NF and higher output power. For reception of the supervisorysignal by the 1RREP 2, a WDM coupler 217 for pumping the firstErbium-doped fiber 211 stage is used to draw the supervisory signalbefore an exclusive receiver 218. This minimizes degradation of the NFbelow 0.2 dB to accomplish an optimum reception of the supervisorysignal.

[0131] For transmission of the supervisory signal by the 1R-REP 2, alight source 219 of 1480 nm wavelength range for the supervisory signalis used to wavelength-multiplex with the main signal before beingtransmitted to a downstream. Wavelength multiplexing of the supervisorysignal with the main signal is made by using a WDM coupler 220 whichalso serves to pump the latter Erbium-doped fiber 216.

[0132] To prevent output of the light booster from decreasing, the WDM(wave division multiplex) coupler 203 for wavelength multiplex of thesurveillance and control signal with the main signal is made to alsoserve as the WDM coupler for laser pumping. In such a way as describedabove, with the surveillance and control signal demultiplexed andmultiplexed at the input and the output of the 1R-REP 2 respectively, aninter-office cable connected to the equipment can be used to inform afailure to the downstream even if the failure is the input signaldisconnection or in the transmission medium within the 1R-REP 2.

[0133]FIG. 17 is a block diagram for the optical transmission system forthe short distance system.

[0134] The short distance system, as shown in the figure, like the longdistance system, uses a modulator integrated light source module 200 of1552 nm wavelength for a transmitting light source. The short distancesystem is different from the long distance system in that a transmitterof the short distance system uses a semiconductor light amplifier 230 asan optical booster to make the transmitter small, and a receiver uses anoptical receiver 231 of small size and low power consumption having asuperlattice APD of low noise and wide frequency response.

[0135] If it has a high optical power input thereto, the optical fiberhas an SBS caused, resulting in degradation of the transmissioncharacteristics. For the CW light, the SBS is caused with the opticalfiber input power higher than +6 dBm. In modulation, the SBS is causedby blight-line spectra contained in the signal light. It is generated ata light power level higher than the one for the CW light.

[0136] To suppress the SBS, the embodiment uses a way that the generatedlaser light is modulated with a low frequency signal to broaden thelight spectra equivalently. The suppression of the SBS by broadening thelight spectra is described in an article entitled “Suppression ofStimulated Brilloiun scattering and Brilloiun Crosstalk by FrequencySweeping Spread-Spectrum Scheme,” Journal Optical Communications, Vol.12, No. 3, pp. 82-85 (1991), A. Hirose, Y. Takushima, and T. Okoshi.

[0137]FIG. 18 is a block diagram for a clock transit system for theoptical transmission system.

[0138] A clock for process of section overhead of transit signals in theLT-MUX 1 and 3R-REP 3, as shown in the figure, is an extracted clocksmoothed by a PLL. The PLL has a time constant which is set in an orderof msec that can almost completely suppress random jitters superimposedthrough the transmission circuit and line. A low-speed wander of thetransmission clock is transferred by a pointer justification feature ofthe section overhead. With these, the 3R-REP 3 can make the repeatwithout accumulation of the jitters, so that it is free of the jitteraccumulation due to continuation of an identical code.

[0139] In transmission of the SDH section overhead, all the sectionoverhead bytes except parts of the first line are scrambled. (FIG. 19shows the parts of the first line, including 4 bytes containing the last2 A1 bytes and first 2 A2 bytes, 64 C1 bytes, and succeeding 2×64 fixedbytes.) This prevents repetition of a fixed pattern as much as hundredsof bytes, reduces a pattern jitter, and averages output of a timingfilter. If a 4-byte synchronous pattern is used, a frame synchronizationprotection is longer than 10 years in average misframe interval for fiveconsecutive forward protection, and is lower than 1% in misframeprobability and rehunting probability for two consecutive backwardprotection.

[0140] 5. Description of 1R-REP

[0141] This section describes the 1R-REP 2.

[0142]FIG. 20 is a block diagram for the 1R-REP. Table 8 charts majorfeatures of the 1R-REP 2. TABLE 8 ITEM DESCRIPTION Main signal Signalwavelength 1.552 μm ± 0.001 μm interface Mean light output +10 to +12dBm Input light level −18 to 0 dBm Noise figure Lower than 7 dB Pumpingmethod Bidirectional pumping of Erbium-doped fiber, with 1.48 μm pumpinglasers. Surveillance and control • Transference of surveillance methodand control signal by 1.48 μm wavelength multiplex. • Implementation ofsurveillance and control section in main signal unit. Physicalimplementation 300 mm high × 3 shelves per method bay (1800 × 795 × 600mm) Cooling method Natural convection, with convection guiding plate of100 mm high. Accommodation of systems Two systems per shelf (one systemcontains both east and west systems) Environmental conditionsTemperature: 10 to 40° C. Humidity: 20 to 80% Input power condition −42to −53 V

[0143] As shown in FIG. 20, the 1R-REP optical transmission systemconsists of two amplifier stages, including an optical preamplifier 301for magnification with a low noise and an optical booster amplifier 320for high power magnification. An output of the optical preamplifier 301is connected to an input of the optical booster amplifier 320. Thisaccomplishes a lownoise, high power output characteristic in a widedynamic range.

[0144] Description of the preamplifiers is ignored here as it wasalready made previously by reference to FIG. 16.

[0145] The 1R-REP 2 can monitor light outputs and intermediate signalpowers and detect opening of the outputs so that it can control andmonitor a gain of each optical amplifier stage. As described previously,the 1R-REP 2 also can receive and transmit the surveillance and controlsignal of 1.48 μm wavelength. The monitor and control and processing thesurveillance and control signal are made by an surveillance signalprocessor/automatic power control circuit 310.

[0146]FIG. 21 is a block diagram for a package construction of the1R-REP 2. The main signal system of the 1R-REP 2, as shown in thefigure, comprises two packages, including a preamplifier package havingthe low-noise optical preamplifier 301 and a booster amplifier packagehaving the high-power optical booster amplifier 320. As will bedescribed later, a single bay having a plurality of shelves, each ofwhich has two systems and the OpS IF as a common section.

[0147] The ground 1R-REP 2, like the LT-MUX 1 and the 3R-REP 3, hasfeatures of preventive maintenance, failure identification, andworkability increase.

[0148] These features facilitate troubleshooting for each 1R repeatersection. As for the 1R repeater section overhead providing a feature ofa surveillance and control communication channel between offices havingthe 1R-REP 2, as described previously, it uses the surveillance andcontrol light of 1.48 μm wavelength.

[0149] The following describes monitor of the 1R repeater section andprocess of the 1.48 μm surveillance and control signal in detail. Itshould be noted that the surveillance and control made by the 1R-REP 2are similarly made by the LT-MUX 1 and the forward pumping opticalpreamplifier 35 and the optical booster amplifier 34 of the 3R-REP 3.

[0150] Table 9 lists surveillance and control items of the 1R-REP 2.TABLE 9 Surveil- Alarm Signal Optical fiber disconnection lance failureMain signal (Preceding REP failure) Loss of surveillance and controlsignal (Preceding REP failure) Surveillance and control signal LOF (CMI)Surveillance and control signal FCS (frame check sequence) errorEquipment Output open failure Main signal transmit failure Surveillanceand control signal transmit failure Optical amplifier equipment failureSurveillance and control equipment failure Power source system failureMonitor Input signal level Intermediate signal level Output signal levelPumping LD temperature Pumping LD bias Surveillance and control LDtemperature Surveillance and control LD bias Gain Control Year and datesetting and reading Output halt and release Failure sectiondetermination

[0151] As shown in FIG. 9, the 1R-REP 2 provides the following processeswith use of surveillance lights and control signals marked with anencircled number in FIG. 20.

[0152] Number {circle over (1)} in FIG. 20 denotes a surveillance lightsignal which is taken by a PF-WDM out of the input light having beencomposed of the main signal light of 1552 nm wavelength and thesurveillance and control light signal of 1480 nm wavelength. Thesurveillance light signal is 3R-processed to convert to electricalsignal by a supervisory signal receiver. The surveillance light signalis used by the automatic power control circuit surveillance signalprocessor 310 to detect the supervisory signal input disconnection.

[0153] Number {circle over (2)} in FIG. 20 denotes a monitor lightbranched from a light output of the low-noise amplifier section by aCPL. The monitor light is used by the automatic power control circuitsurveillance signal processor 310 to control the gain, to monitor theinput state, and to monitor the intermediate power.

[0154] Number {circle over (3)} in FIG. 20 denotes another monitor lightbranched from a light output of the high-power output amplifier sectionby another CPL. This monitor light is taken out through a BPF. Themonitor light is used by the automatic power control circuitsurveillance signal processor 310 to control the gain and to monitor theoutput state.

[0155] Number {circle over (4)} in FIG. 20 denotes still another monitorlight branched through the CPL from a light reflected from the outputend. This monitor light is used by the automatic power control circuitsurveillance signal processor 310 to detect opening of the output.

[0156] Number {circle over (5)} in FIG. 20 denotes control signals usedby the automatic power control circuit surveillance signal processor 310to stabilization-control the output of the pumping source and to monitorLD states.

[0157] Number {circle over (6)} in FIG. 20 denotes the surveillance andcontrol signal sent from the automatic power control circuitsurveillance signal processor 310. The surveillance and control signalis converted to an optical signal by the surveillance and control lightsource of 1480 μm wavelength. The optical signal is composed with thelight output of the high-power output amplifier by the BB-WDM. Thesurveillance and control signal is used to monitor the surveillancelight source LD state and to detect the supervisory signal transmitfailure.

[0158] It is needed for the 1R-REP 2 that depending on the surveillanceresults and the like of the surveillance items, as described above,identification should be made for the transmission line alarms as toloss of the main signal, transmit failure of the main signal, loss ofthe supervisory signal, the input fiber disconnection, and the like.Such failure points can be identified by a judgement logic comprehendedof the surveillance items {circle over (1)}, {circle over (2)}, and{circle over (3)}. Also, the 1R-REP 2 can detect the equipment failuresof the optical amplifier repeater section for preventive maintenance ofequipment. Further, the 1R-REP 2 has external control features of outputshutdown for safe work.

[0159] Furthermore, the 1R-REP 2, as described above, can not only sendthe surveillance and control information to the downstream equipmentdepending on the surveillance results of the surveillance and controlitems, but can also repeat to transfer to the downstream equipment thesurveillance and control information received from the upstreamequipment.

[0160] Still furthermore, the embodiment does not only inform any of thefailures of the 1R-REP 2 to the downstream, but also facilitatesjudgement of a failure point in each of the 1R repeater section and alsomaintains on the inter-office fiber the surveillance and controlcommunication channel between the office having the 1RREP 2. To dothese, the surveillance and control signal light is terminated once foreach 1R-REP 2 before being repeated to the downstream through automaticpower control circuit surveillance signal processor 310 to transfer.This has the advantage that the surveillance information can betransfered by a single wavelength even if the number of repeaters isincreased.

[0161] In turn, if the wavelength used for the supervisory signal is outof the range of the optical amplifier, this will not cause saturation inthe optical amplifier, and thus will not affect the main signal. Forthis reason, the light of 1.48 μm is used as described above. This lightprovides as little a transmission line fiber loss as the main signalwaveform, and allows using a WDM (wave division multiplex) coupler tocompose and divide the pumping light in common.

[0162] The CMI code is used to send the surveillance and control signal.With the CMI code used, a dc component and zero continuation can besuppressed. Also, a frame synchronizing circuit can be made up ofrelatively few components by a frame synchronization method of codeviolation.

[0163]FIG. 22 is a format for the surveillance and control signal foruse in the surveillance and control of the 1R-REP 2.

[0164] The embodiment accomplishes the feature of remote control in away as that shown in FIG. 22, the surveillance and control signal usedis of a 48 byte-long frame for period of 1 msec at a rate of 384 kb/sec,and the DCC of 192 kb/sec is maintained within the surveillance andcontrol signal. The frame has 1 byte for information of severe failuresevery period of 1 msec. This accomplishes the feature equivalent to theF1 byte of the SDH.

[0165] 6. Description of LT-MUX

[0166] This section describes the LT-MUX 1 in detail.

[0167]FIGS. 23 and 24 are block diagrams for hardware constructions ofthe long distance system related to the embodiment. Table 10 chartsmajor features of the LT-MUX 1. As for differences of the hardwareconstruction of the LT-MUX 1 for use in the short distance system fromthose of the long distance system, they will be described below asnecessary. TABLE 10 DESCRIPTION FOR FOR LONG- SHORT- DISTANCE DISTANCEITEM SYSTEM SYSTEM Intra- Transmission rate 155.52 Mb/sec (STM-1) ×office 64 series or 622.08 Mb/sec inter- (STM-4) × 16 series. faceTransmission line code Scrambled binary NRZ. Error rate Lower than 10⁻¹¹Light source wavelength 1.31 μm +0.05 μm to −0.04 μm (STM-1); 1.31 μm+0.05 μm to −0.05 μm (STM-4) Average light output −17 to −11 dBm(STM-1); −15 to −8 dBm (STM-4) Maximum detectable power Higher than −8dBm Minimum detectable power Lower than −24 dBm (STM-1): Lower than −23dBm (STM-4) Redundancy configuration 1 + 1 dual Inter- Transmission rate9953.28 Mb/sec (equivalent office to STM-64) inter- Transmission linecode Scrambled binary NRZ (non-return face to zero) Error rate Lowerthan 10⁻¹¹ Light source wavelength 1.552 ± 0.001 μm, with chirpingparameter a being 1.0 ± 0.2 Average light output +10 to +12 dBm +5.6 toDirect LT connection: +6.6 dBm +15 to +16 dBm Maximum detectable powerHigher than −7 dBm Higher than −10 dBm Minimum detectable power Lowerthan −27 dBm Lower than −23 dBm Redundancy configuration Mesh switchingusing virtual ring at VC-¾ level Surveillance and control methodSurveillance control by OpS inter- face. 1R-REP surveillance and controlby 1.48 μm wavelength multiplex. Physical implementation method 300 mmhigh with 4 shelves (1800 × 395 × 600 mm) Cooling method Push-pull typeforced air cooling, with large fan. Accommodation of systems Two systemsper rack. Environmental conditions Temperature: 10 to 40° C. Humidity:20 to 80% Input power condition −42 to −53 V

[0168]FIG. 23 is for the inter-office transmission line of the LT-MUX 1.FIG. 24 is for the intra-office transmission line of the LTMUX 1. TheLT-MUX 1, as shown in the figures, comprises a high-speed IF shelf 600,a low-speed IF shelf 700, a supervisory control/OpS 650, an OH IF 660,and a clock section 670.

[0169] The high-speed IF shelf 600 comprises an OPTAMP S 601 havingfeatures as the optical booster amplifier 14 of the transmitting system,an OPTAMP R 603 having features as the optical preamplifier 15 of thereceiving system, a 10G IF S 602, a 10G IF S 604, and a plurality of S0H605 boards. The lowspeed IF shelf 700 comprises a plurality of SELs 701,and a plurality of intra-office IF 702 packages. The high-speed IF shelf600 and the low-speed IF shelf 700 are connected together by anintra-equipment interface of 155 Mb/sec rate.

[0170] The embodiment has a high-speed interface 600-1, an SEL 701-1,and an intra-office interface 702-1 to have a redundancy feature of 1+1section switching type. These blocks are not needed if the sectionswitching is not made.

[0171] Tables 11 and 12 chart the features of the LT-MUX 1. TABLE 11BLOCK ITEM NAME FEATURE NOTE 1 10G IF-S (1) Optical boosteramplification OPTAMP-S (2) 1R repeater surveillance and control signallight transmission (3) STM-64 signal E/O conversion (4) 10 GRz PLL (5)STM-64 RSOH transmission (6) Physical rate conversion of 155 Mb/sec to10 Gb/sec 2 10G IF-R (1) Optical preamplification OPTAMP-R (2) 1Rrepeater surveillance and control signal light reception (3) STM-64signal D/E conversion and clock extraction (4) STM-64 RSOH termination(5) Physical rate conversion of 10 Nb/sec to 155 Gb/sec 3 SOH (1) STM-64MSOH process (2) Pointer conversion of AU-3, AU-4, and AU-4-4c (3) POHmonitor of VC-3, VC-4, and VC-4-4c and line test 4 SEL (1) System0/system 1 selection of STM-1/STM-4 intra-office transmission line (2)System 0/system 1 phase matching of VC-3, VC-4, and VC-4-4c (hitlessswitching) (3) APS protocol control for intra-office transmission lineswitching 5 Intra-IF STM-1 or STM-4 intra-office transmission linetermination (1) E/O and O/E conversions (2) SOH process (3) Pointerconversion of AU-3, AU-4, and AU-4-4c (4) POH monitor of VC-3, VC-4, andVC-4-4c and line test Number of accommodated lines is STM-1 × 8 or STM-4× 2 per board. 6 SVCONT (1) Information collection in (LIF) low-speed IFshelf, operation of performance surveillance information, and event madeof alarm data • Intra-office section • AU pathbus • Surveillance inequipment (2) Alarm priority processing and failure determination (3)Distribution and status reading of control information in shelf •Software strap of intra-office section • AU line test • Selected statusof redundancy system

[0172] TABLE 12 ITEM BLOCK NAME FEATURE NOTE 7 SVCONT (HIF) (1) 10Ghigh-speed transmission IF, surveillance information collection ofsubmarine repeater, operation of performance surveillance information,and event made of alarm data IR repeater section Multiplex section AUpath Surveillance in equipment (2) Alarm priority processing and failuredetermination (3) Distribution and status reading of 10G high-speedtransmission line IF and repeater control information Software strap AUline continuity check Control and status reading of repeater 8 SEMF (1)OpS message conversion (2) Time management and history processing (3)Emergency start-up of backup memory (4) Switching control of clocksection and SVCONT (5) Processing of common system alarm 9 OpS IF (1)OpS message communication processing 10 RMT IF (1) Remote surveillanceand control communication by DCC of multiples section overhead (MSOH) 11CREC (1) B/U conversion of 64 kHz + 8 kHz clock 12 CDIS (1) Clockgeneration (PLL) and distribution in equipment 13 CSEND (1) Transmissionof extracted clock 14 OH IF (1) Input/output of overhead signal outsideequipment (2) OAM processing by overhead signal

[0173]FIG. 25 is a relationship of multiplex and demultiplex between theSTM-64 frame and the STM-1×64 supported by the LT-MUX.

[0174] A 10G E/O 610 of a 10G IF S 602 and an OPTAMP S 601 thetransmitter of the LT-MUX 1, and a 10G O/E 611 of a 10G IF R 604 and anOPTAMP R 603 form the receiver of the LT-MUX 1.

[0175] The following describes the transmitter and the receivermentioned above.

[0176]FIG. 26 is a block diagram for the transmitter of the LT-MUX 1forming the long distance system.

[0177] The transmitter, as described previously, comprises the 10G E/O S610 having the high-speed multiplex circuit 682 for converting a 622Mb/sec, 16-parallel signal to 9.95 Gb/sec signal in a way of a 16-bitmultiplex (STM-64) and the electro-optic converter 681 and the OPTAMP S601 which is an optical amplifier.

[0178] As shown in the figure, the embodiment uses an externalmodulation of electric field absorption type for electro-opticconversion. The OPTAMP S 601 is formed of an optical fiber amplifier.The optical fiber amplifier is separately implemented in its respectivepackage in view of its occupying area and consumption power. Thetransmitter further has a temperature control circuit 683 and an opticaloutput control circuit 684 so that the long-distance transmission can bemade even if environmental conditions around the electro-optic converter681 and the OPTAMP S 601 change. Description of the transmissionoperation is ignored as it was already made by reference to FIG. 16.

[0179]FIG. 27 is a block diagram for the transmitter of the LT-MUX 1forming the short distance system.

[0180] The transmitter of the LT-MUX 1 forming the short distancesystem, as described in the figure, has no OPTAMP S 603. The 10G IF S602, unlike that of the long distance system, uses a semiconductoroptical amplifier of preferably smaller size and lower power consumptionfor optical amplification in the 80-km transmission. The semiconductoroptical amplifier can be made to occupy as narrow an area as themodulator with LD, and can be implemented in the 10G IF S 602 shelf. Theembodiment, as shown in the figure, uses a modulator of an electricfield absorption type for the external modulator. The electric fieldabsorption type modulator is integrated to a module of small size aselectric field absorption type device are structurally practical tointegrate with the laser diode for the light source.

[0181]FIG. 28 is a block diagram for the receiver of the LT-MUX 1forming the long distance system.

[0182] The receiver comprises the OPTAMP R 603 which is an opticalamplifier and the 10G O/E 611 having an opto-electric converter 693 anda high-speed demultiplex circuit 692. The OPTAMP R 630, as shown in thefigure, is made up of an optical fiber amplifier having an opticalpreamplifier feature, and is separately implemented in its respectiveboard. The opto-electric converter 693 is made up of a front module, anamplifier, a timing extractor, and an dicision circuit. The highspeeddemultiplex circuit 692 converts the 9.95 Gb/sec signal to 622 Mb/sec ina way of parallel demultiplex. Description of the reception operation isignored as it was already made by reference to FIG. 16.

[0183]FIG. 29 is a block diagram for the receiver of the LT-MUX 1forming the short distance system.

[0184] The short distance system is different from the long distancesystem in that the short distance system has no OPTAMP R 603 and uses anAPD 694 for opto-electric conversion. As its APD 694 is capable ofhigher sensitive reception than Pln-PD, the short distance system needsno optical amplifier, thus resulting in a smaller system.

[0185] In turn, if the LT-MUX 1 and the ADM switch are combined to formthe small scale switching node 120 as in FIG. 6, the high-speed IFshelf, the low-speed IF shelf 700, and a 40G switch shelf are combinedas shown in FIG. 30. The 40G switch shelf comprises multiplexingcircuits 901 for multiplexing the input signals to feed to time-divisionswitches 903, the time-division switches 903, and demultiplexingcircuits 902 for demultiplexing the signals from the time-divisionswitches 903. An interface of the multiplexing circuits 901 and thedemultiplexing circuit 902 is the intra-equipment interface.

[0186] In turn, the signal from the transmission line is processed bythe high-speed IF shelf 600 before being directly input to the switchwithout the low-speed IF shelf 700. The signal to be dropped into theoffice, is connected to the low-speed IF shelf 700. As for the signal tobe passed to the another node, it is connected to the high-speed IFshelf 700 before being fed out to another node. That is, the signal fromthe transmission line is not converted as to interface by the lowspeedinterface before being connected to the switch, as usual.

[0187] But, the high-speed IF shelf 600 is directly connected with theswitch. This can make the equipment smaller.

[0188] If the small scale switching node 120 or the large scaleswitching node 110 is constructed to have the cross-connection switchfeature, the 40G switch in FIG. 30 is replaced by a multi-stage switchconfigured of a plurality of 40G switch shelves.

[0189] As described above, the embodiment can appropriately combine thehigh-speed IF shelves 600, the low-speed IF shelves 700, and the 40Gswitch shelves 900 in the building block way. This allows accomplishmentof a desired equipment with use of the common shelves in a minimizedconstruction. Also, the embodiment allows accomplishment of the 3R-REP 3by combination of the boards of the high-speed IF shelf 600 as will bedescribed later.

[0190] The following describes the surveillance and control system forthe LT-MUX 1.

[0191]FIG. 31 is a block diagram for extracted parts serving to thesurveillance and control system for the LT-MUX 1.

[0192]FIG. 32 lists features of the functional blocks.

[0193]FIGS. 13, 14, 15, and 16 chart features of the surveillance andcontrol system.

[0194] In FIGS. 31 and 32, the SVCONT 703 is installed for eachlow-speed IF shelf. The SEMF 651, the OpS IF 652, and RMT IF 653 areequipped in the common a shelf as will be described later. TABLE 13FEATURE DESCRIPTION NOTE 1 Path setting (1) Switch control memoryControl system is updated to set path according to the control messagefrom the operation system outside equipment. (2) Path setting unitsinclude: a. Units of VC-3 b. Units of VC-4 c. Units of VC-4c (600 M atmax) (3) This feature is an option for implementation of cross-connection feature 2 Software strap (1) Control register of each Controlsystem setting section in equipment is NOTE 1: updated to set operationUpon use of mode (software strap) section according to controlprotection message from operation feature system outside equipment. (2)Major software strap features include: a. Transference approval orinhibition of transmission line system alarm b. Threshold of error ratedegradation c. Protection time of switching control (NOTE 1) 3 Path test(1) Test access point is set to Control system confirm continuity andset quality in units of path according to the control message from theoperation system outside equipment. (2) Path testing units include: a.Units of VC-3 b. Units of VC-4 (3) Test pattern conforms to CCITTRecommendation 0.151 4 Redundancy (1) The operation system switchesControl system system over functional components of Surveillanceswitching in equipment having redundancy system equipment form accordingto the control message from the operation system outside equipment.(Forced switching) (2) As results of equipment diagnosis, the operationsystem switches over to the protection side from function component ofequipment judged at failure. (Autonomous switching) (3) Operation modesof redundancy system include: a. Automatic mode, allowing autonomousswitching b. Forced selection mode c. Lock-out mode

[0195] TABLE 14 FEATURE DESCRIPTION NOTE 5 Configuration (1)Implementation states of Surveillance management functional componentsof system equipment are monitored, and the database for con- figurationmanagement in the control system is automatically updated as needed. (2)When the implemented functional component does not logically match withthe physical implementation position, then an alarm is issued. (3)Management units for functional components of equipment include: a.Board b. Board group c. Shelf 6 Alarm (1) Transmission line systemalarms Surveillance transference are collected from line termi- systemnation feature blocks and path connection feature blocks to detectgeneration and restoration of alarms before transmission line systemalarms are made into an event. (2) On basis of diagnosis results ofequipment failure, equipment alarms are made into an event. (3) Contentsof these alarms made into a event are converted to messages before beinginformed to external surveying operation system. 7 Performance (1)Performance information, such Surveillance management as a bit error,are collected system from line termination feature blocks and pathconnection feature blocks to calculate and generate performancemanagement information for transmission lines and paths. (2) Theperformance management information includes: a. CV (code violation) b.ES (errored second) c. SES (severely errored second) (3) Types ofregisters for history management includes: a. 1-sec register b. 15-minregister c. 1-day register

[0196] TABLE 15 FEATURE DESCRIPTION NOTE 7 Equipment (1) Failuresurveillance infor- Surveillance diagnosis mation is collected fromsystem functional components of equipment, and a specific functionalcomponent having a hardware failure generated is identified on the basisof the failure judgement map provided in the surveillance and controlsystem. (2) Specific functional component having a hardware failuregenerated is logically disconnected, and the operation system switchesover from the functional component of redundancy configuration to theprotection side. (3) Equipment information is sent out to informexistence of a functional component having a failure generated. 9Section (1) If a section failure happens, Control system switchingsection switching is controlled Surveillance control on the basis of MSPprotocol. system (2) Switching system includes the MPS: Multi- followingmanners: plan a. 1 + 1 (without switch-back) Section b. Bi-directionalswitching Protec- (3) Switching is caused by tion include: a. SFswitching (LOS, LOF, S-AIS, and hardware failure) b. SD switching (MER)c. Forced switching (OpS command) (4) This feature is optional. 10 Pathswitching (1) If a path failure is detected Control system control withgeneration of a failure Surveillance in the ring meshed network, systemsection switching is con- PGP: Path trolled on the basis of MSP Groupprotocol. Protec- (2) Switching system includes the tion followingmanners: a. 1 + 1 (with switch-back) b. Bilateral switching (3)Switching is caused by include: a. SF switching (LOP, P-AIS, andhardware failure) b. SD switching (MER) c. forced switching (OpScommand) (4) This feature is optional for implementation of cross-connection feature.

[0197] TABLE 16 FEATURE DESCRIPTION NOTE 11 History (1) Variety ofevents generated Control system management as to transmission lineSurveillance received signals and system equipment statuses are recordedand managed as history information. (2) History information to bemanaged includes: a. Redundancy system switching history b. Signalperformance history c. APS information changing history 12 Backup (1) Ifthe operation state in Control system information equipment is changed,then NOTE 1: management the changed state is With use of automaticallyrecorded in cross- nonvolatile memory as the connection latestinformation. feature (2) Information to be recorded includes: a.Operation information of redundancy system b. Information of softwarestrap c. Path setting information (NOTE 1) (3) The following processesare made with the control message from the control operation system a.Update of backup information b. Comparison with statuses in equipment c.Initialization of backup information 13 Emergency (1) If it is poweredon, equip- Control system start-up ment is autonomously started up foropera- tion on basis of backup information. 14 Communication (1) Controlis made on com- Control system control munication with the Surveillanceoperation system outside system equipment. (2) Communication is of amessage form and has a protocol system on basis of the Q interface ofCCITT Recommendations. (3) Two independent communication links areprovided, including the control system and surveillance system. 15 OpSmessage (1) Control information of Control system conversion messagereceived from Surveillance operation system is system converted to thecommand form specific to equipment. (2) Control information andsurveillance information of the command form specific to equipment areconverted to information of message form before being sent to theoperation system.

[0198]FIG. 33 is a block diagram for the redundancy configuration of thetransmitting system in the LT-MUX 1. FIG. 34 is a block diagram for theredundancy configuration of the receiving system in the LT-MUX 1.

[0199] In general, operations including AU pointer conversion arenonhitlessly switched. To make this hitless, a hitless switching processis needed. In the embodiment, in view of the balance of the featuresprovided in the whole equipment, the AU pointer conversion process isprovided in the intra-office interface and the high-speed interfaceunit. In the SEL 701 between these is provided a hitless switchingprocess feature section which will be described later. As shown in thefigures, simplex sections are optical booster amplifier 601, 10G IF-S602 and the SOH 605 in the operation form without the 1+1 sectionswitching in the 10 Gb/sec transmission line.

[0200] As the intra-office interface is an interface to be connectedwith an existing intra-office equipment, the redundance configurationfollows the manner of the existing equipment. That is, the redundanceconfiguration is made of the 1+1 section switching type of system0/system 1 without switch-back. The board for the intra-office interfaceaccommodates a plurality of highways. Auto-switching at failure is madein units of transmission line. The intra-office interface board,therefore, has working highways and waiting highways mixed therein. Forthis reason, for interface package maintenance, a hitless forcedswitching is needed which will be described later.

[0201] The SEL 701, as shown in FIGS. 23 and 24, is arranged so that itcan be added or removed depending on the situation of transmission lineaccommodation. The SEL 701, therefore, is arranged so that it can beautomatically switched in units of package in the 1+1 way. Note that ifthe hitless forced switching which will be described later is made forthe SEL 701, this is hitlessly made by the hitless switching processsection.

[0202] Now, the following describes the hitless switching process.

[0203]FIG. 35 is a block diagram for construction of the hitlessswitching process feature section for transmission line. Table 17 listsfeatures of functional blocks of the hitless switching process featuresection. TABLE 17 NO. ITEM FEATURES 1 AU pointer AU pointer byte and AUstuff operation termination are read. It is instantaneously taken inwithout protection of consecutive coincidence three times. 2 2 × 2 SELSelector for passing delayed system through, but storing precedingsystem into VC buffer. 3 VC buffer FIFO memory for delaying precedingVC-3, VC-4, and VC-4-4c data. Adjustable distance difference is 4 km. 4VC buffer writing Writing address counter for VC control buffer. OnlyVC-3, VC-4, and VC-4-4c data of input signal are written according todetection of AU stuff. 5 VC buffer reading VC buffer is read in line toAU stuff of control the delayed system. If delay insertion is needed toincrease in phase synchronizing pull-in course, positive stuff is added.If it is needed to decrease, negative stuff is added. 6 Delay insertionDelay insertion of FIFO is calculated calculation through calculation ofthe writing address minus reading address. 7 Phase differenceTransmission delay difference detection is detected by comparison of AUpointer values. 8 Delay insertion Result of delay insertion calculationis control compared with result of phase difference detection. If it isnecessary to increase delay insertion, positive stuff is added on VCbuffer reading side. If it is necessary to decrease delay insertion,negative stuff is added on the vc buffer reading side. 2 × 2 SEL iscontrolled depending on the direction of the delay differencegeneration. 9 Pointer calculation New pointer value is calculated bycomparison of the VC in-put phase of the VC buffer with output framephase. 10 Pointer insertion New pointer value is written in vc bufferoutput signal. Following specific patterns are written in predeterminedpositions. (1) On generation of stuff: Inversion of bits 1 and 0. (2) Onjump of pointer: Sending of NDF pattern. (3) On AU-4 or AU-4-4c: CIconcatenation indicator). (4) On sending of P-AIS: All 1 of all bytes.

[0204] As depicted in Table 17, the hitless switching process featuresection makes the received data, including VC-3, VC-4, and VC-4-c data,of the system having less transmission delay of systems 0 and 1 delay inFIFO memory (VC buffer) as necessary. This makes contents of the outputsignals of both systems coincide. Detection of the transmissiondifference is made by comparison of the pointer values. Adjustment ofthe delay insertion of the FIFO is made with stuff operation of the AUpointer so gradually that the signal of the working system will not behit while the phase synchronizing pull-in is made in maintaining theprotection system. In writing into the VC buffer, the AU pointer isterminal once before only the VC-3, VC-4, and VC-4-c data are written inthe VC buffer. In reading from the VC buffer, on the other hand, readingis made along with the operation of the AU stuff in line with that ofthe AU stuff in the delayed line. In a phase synchronized state, thus,the system 0 can be made to coincide with the system 1 perfectly notonly in the phases of the output VC signals, but also the timings of theAU stuffs. This means that the hitless switching can be made securelyeven if the frequency of the AU stuff is higher.

[0205] The VC buffer is a kind of AU pointer converting circuit. At thetime of output, a new AU pointer value is calculated before beinginserted into the AU. The calculation principles are the same as thoseof the usual pointer converting circuit. As the adjustable transmissiondelay difference is 4 km, the process cannot only be applied to theintra-office transmission line, but also to a short or intermediateinter-office transmission line. Thus, in the SEL, the hitless switchingprocess feature section is constructed so that it cannot be used forswitching the intra-office interface, but also for switching the 10Gb/sec transmission line interface.

[0206] 7. Description of 3R-REP

[0207]FIG. 36 is a block diagram for a construction of the 3R-REP 3.Table 18 lists features of functional blocks of the 3R-REP 3. TABLE 18ITEM DESCRIPTION Main signal Transmission rate 9953.28 Mb/sec(equivalent to interface STM-64) Transmission line Scrambled binary NRZcode (non-return to zero) Error rate Lower than 10⁻¹¹/repeater. Lightsource 1.552 μm ± 0.001 μm wavelength Average light +10 to +12 dBmoutput Maximum detectable Higher than −7 dBm power Minimum detectableLower than −27 dBm power Surveillance and control method Surveillanceand control signal transference by 1.48 μm wavelength multiplexedsignal. Implementation of surveillance control section in main signalunit. Physical implementation method 300 mm high with 4 shelves perframe (1800 × 795 × 600 mm). Cooling method Push-pull type forced aircooled type, with large fan. Accommodation of systems One system pershelf, with one bidirectional system of west and east. Environmentalconditions Temperature: 10 to 40° C. Humidity: 20 to 80%. Input powercondition −42 to −53 V

[0208] The 3R-REP 3 makes regeneration through its opticalpreamplication, O/E conversion, E/O conversion, and optical boosteramplification. The 3R-REP 3 also makes the surveillance, alarmtransference, and remote maintenance for the 1R repeater section and the3R repeater section with use of the 1.48 μm surveillance and controllight and the RSOH (regenerator section overhead. The boards used in themain signal system are all the same as those of the LT-MUX 1.

[0209] 8. Implementation of the 1R-REP, LT-MUX, and 3R-REP

[0210] The following describes implementation of the 1R-REP 2, LT-MUX 1,and 3R-REP 3.

[0211] First, implementation of the 1R-REP 2 is described below.

[0212]FIG. 37 is a front view for an implementation of the 1R-REP 2.

[0213] A rack of the embodiment, as shown in the figure, has threeshelves each of which contains two 1R-REP 2 systems, or six 1RREP 2systems in total. Each system comprises two subsystems: the repeaters301 and 302. For an unattended office which needs remote monitor andcontrol, these are implemented in the same shelf as the system to whichthe OpS IF 651 and the like serve. Note that a power source board 810 isfor the optical preamplifier 301 and the optical booster amplifier 320.

[0214]FIG. 38 is structures of the optical preamplifier 301 and opticalbooster amplifier 320 forming a single 1R-REP 2 system. The opticalpreamplifier 301 and the optical booster amplifier 320, as shown in FIG.37, occupy two-fold and four-fold widths in reference to a standardboard width respectively, or six-fold width in total. They are naturallyair-cooled. Note that a TEC drive circuit in FIG. 38 is a circuit addedto the pumping light source to control a temperature adjustment forthermoelectron cooling devices.

[0215] Implementation of the LT-MUX 1 is described below.

[0216]FIG. 39 is a front view for an implementation of the LT-MUX 1.

[0217] The construction shown is for accomplishing the transmission line1+1 redundancy system switching. The functional boards of the high-speedIF unit 600 and the low-speed IF unit 700, as shown in the figure, areall doubled as in a working system 0 and a waiting system 1. FIG. 40 isa front view for an implementation of two systems of the LT-MUX 1 in asingle rack without the redundancy configuration.

[0218] The 10G IF R 604 package and the 10G IF S 602 board, as shown inthe figure, are of two-fold wide as these have many components.Similarly, the OPTAMP R 603 board and the OPTAMP S 601 board are oftwo-fold wide.

[0219]FIG. 41 is a front view for an implementation of the LT-MUX 1 forconstructing the small scale switching node 120 with the 40G switch unitbuilt in as shown in FIG. 6b.

[0220] In this case, as shown in the figure, are implemented twohighspeed interface units 600, a duplexed 40G switch unit 900, and aduplexed low-speed IF unit 700. The 40G switch unit 900, as shown inFIG. 42, is three-dimensionally constructed in view of the flow of itssignals. That is, a plurality of boards MUX/DMUX containing a pluralityof multiplex/demultiplex circuits 901 and 902 and a time-division switch(TSW) 903, are three-dimensionally connected together with use of asubpanel for a time switch unit. This construction can be made small.

[0221] Implementing the 40G switch into the shelf is made in a way thatthe TSW 903 is put in front, the 40G switch unit 900 is put into theshelf, and the MUX/DMUX board 901/902 is connected with other units onthe rear side of the shelf.

[0222]FIG. 43a is a front view for an implementation of the LT-MUX 1 forconstructing the large scale switching node 110 with a multi-stageswitch meshed network of a plurality of the 40G switch units builttherein.

[0223] In this case, as shown in the figure, a plurality of racks havethe 40G switch units, the high-speed IF units 600, and the lowspeed IFunits 700 built therein so that the high-speed IF units 600, and thelow-speed IF units 700 can be connected with the switch multi-stagenetwork.

[0224] Finally, FIG. 44 is a front view for an implementation of the3RREP 3.

[0225] As shown in the figure, a single rack has four shelves each ofwhich contains a main signal board, including OPTAMP R 603, 10G IF R604, 10G IF S 602, and OPTAMP S 601 packages, and a common section, suchas an OpS IF 651. This construction allows a single shelf to completeall the features of a single equipment. It is possible to easilyincrease or remove the equipment in shelf units as needed.

[0226] As described so far, the present invention can flexibly build upthe optical transmission system depending on capacities and functionrequired.

What is claimed is:
 1. An optical transmission equipment which transmitsan amplified optical data signal and an optical surveillance signal,comprising: a doped fiber to which an optical data signal is input andwhich outputs said amplified optical data signal; a surveillance signalsource which outputs said optical surveillance signal; and a couplerwhich multiplexes said amplified optical data signal and said opticalsurveillance signal; wherein a wavelength of the optical surveillancesignal is an output of an amplification wavelength range of said dopedfiber, and wherein the transmission loss of said optical surveillancesignal in a transmission fiber is substantially the same as thetransmission loss of said optical data signal in said transmissionfiber.